Various anatomical exercise and therapy devices for exercising or conducting specific therapy movements of different muscle groups of a patient are well known in the art. As an example, continuous motion passive exercise machines have now become the standard of care for rehabilitation of joint injuries of injured or surgical patients.
In general, a passive motion exerciser moves a body part such as an arm or foot through a range of motion. This simulates the operation of the muscles and joints associated with the body part. Such passive motion exercisers may be continuous in motion and driven by electric motors or other continuous drive means. U.S. Pat. No. 4,355,633 to Heilbrun discloses such a passive exercise apparatus for exercising the shoulder joint. French Patent No. 2,635,457 to Stef discloses a passive exercise apparatus for the foot and ankle.
A problem with such passive exercise devices, as they are related to ankle and foot rehabilitation, is that in general, the prior art continuous-motion ankle-foot exercise devices do not compensate for the complex anatomical construction of the ankle and foot. Movement of the foot relative to the leg involves the ankle joint as well as the subtalar joint. The axis of the ankle joint and subtalar joint are not coincident to one another. These axes are in fact, located at different angles to the plane and longitudinal axis of the foot. Most prior art passive exercise devices accommodate only the ankle joint.
In FIGS. 1 and 3, the subtalar axis is denoted as S--S. As shown in FIG. 1, the subtalar axis S--S is situated about 45.degree. from the plane of the foot and as shown in FIG. 3 about 84.degree. off the longitudinal axis L--L of the foot. The ankle axis is denoted as A--A in FIGS. 1 and 3. The ankle axis A--A is situated about 13.degree. off the horizontal plane of the foot and as shown in FIG. 3 about 84.degree. off the longitudinal axis L--L of the foot.
As shown in FIG. 1, the ankle joint is formed by the articulation of two bones of the leg, the tibia and fibula, relative to the talus. The talus is the second largest tarsal and the main weight bearing bone of the articulation. The subtalar joint is formed by the articulation of the talus with the largest tarsal the calcaneus.
In FIGS. 2-6, the different motions of the foot are shown. As shown in FIG. 2, movement of the foot from a neutral position and away from the leg is referred to as plantarflexion. Movement of the foot from a neutral position and towards the leg is referred to as dorsiflexion. In general, plantarflexion and dorsiflexion motion involve movement about the ankle joint.
As shown in FIG. 3, the foot may also move from a neutral position towards the center of the body (adduction) or away from the center of the body (abduction). Dorsiflexion has a component of abduction, plantarflexion has a component of adduction.
Additionally, as shown in FIGS. 4-6, the ankle may also be moved from a neutral position (FIG. 5) by turning outward, which is denoted as eversion (FIG. 4), or by turning inward which is denoted as inversion (FIG. 6). In general, eversion and inversion motion of the foot involve movement about the subtalar joint.
As previously stated, most prior art passive exercise apparatus are directed only to ankle joint motion and do not include subtalar joint motion. Moreover, prior art continuous motion passive exercise devices do not allow the different axes of rotation to be isolated (i.e. pure ankle joint motion or pure subtalar joint motion). Consequently, all of the muscles associated with the foot and ankle are not exercised and the different joints cannot be specifically isolated. A total workout of the foot muscles is thus not achieved. Additionally, the muscles of the foot responsible for plantarflexion and dorsiflexion are stronger than the muscles which perform inversion and eversion. Inadequate rehabilitation of the muscles responsible for inversion and eversion may accentuate this imbalance.
The ankle-foot exerciser of the invention, on the other hand, is constructed to passively exercise both the ankle and subtalar joints and allow the muscles associated therewith to follow a natural anatomic range of motion. Additionally, the ankle-foot exerciser of the invention may be adjusted to achieve either pure ankle motion, pure subtalar motion or a combination of both.